There's a reason why optometrists say you should regularly replenish your contact lens solution and throw out your lenses after the expiry date. Last year, a young woman contracted an eye infection after using tap water to dilute her cleaning solution, and while wearing contact lenses that were two months past their expiry date. Subsequent analysis of her lens solution revealed an entire cornucopia of microorganisms that were spawned from a single amoeba, including a giant virus that was also infected with a virus — and a piece of DNA that was capable of infecting both of them.

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Thankfully, the woman's condition, keratitis, was not serious and was easily treatable — but the subsequent analysis of her contaminated lens solution was quite revealing, if not disturbing.

The research, which was conducted by Bernard La Scola and Christelle Desnues, was initially concerned with an amoeba they found in the fluid. But after looking at the amoeba more carefully, the researchers discovered that it hosted two different microorganisms, including a giant virus that had never been seen before (what is now called the Lentille virus).

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This Lentille virus, after infecting the amoeba, created a kind of "virus factory" where its genetic material was copied, thus spawning new viruses that were architected from its genetic script.

Now, if this wasn't surprising enough, the researchers also discovered that the Lentille virus was also infected with a virus, what's called a virophage. This virus-within-a-virus, named Sputnik 2, is only capable of reproducing in cells infected by other viruses (in this case, the infected amoeba). Amoebas that are infected with this virus continue to release virophage particles, which means the virus can continue to infect other amoebas on their own.

But there's still more: Both the giant Lentille virus and Sputnik 2 virophage contained even smaller parasites called transpovirons — highly mobile chunks of DNA that can relocate themselves into the genomes of viruses and tuck themselves away inside of virophages.

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So, in summary, the researchers discovered that a transmissible DNA sequence managed to find its way into a virophage (and potentially the giant virus itself), which in turn latched onto a giant virus, which then infected an amoeba — an amoeba that eventually found its way into the eye of a 17-year old girl. You can read the entire study at PNAS.